Small sound conversion devices, in which a speaker closely placed over an ear or an eardrum converts an electrical signal output from a reproducing device or a receiver into a sound signal, that is, earphones have been widely used. The sound reproducing device of this sort outputs a sound to be heard by only the listener who wears the device, and thus is provided for use in various environments.
Many of the currently used earphones have a shape used by being inserted in the ear of the listener. For example, an inner ear-type earphone has a shape used by being hooked on the pinna of the listener. Further, a canal-type earphone has a shape used by being deeply inserted into the ear cavity (ear canal), and many of the canal-type earphones are sealed types in structure and are relatively favorable in sound insulating properties, and thus have an advantage that a wearer can enjoy music in a noisy place.
The canal-type earphone includes, as basic configuration elements, a speaker unit that converts an electrical signal into a sound signal and an approximately cylindrical housing (case) that is also used as a sound tube, and the speaker unit is attached to one end of the housing (outside the ear canal). The housing is provided with a radiation outlet through which aerial vibration generated in the speaker unit is radiated to the ear canal and transmitted to the eardrum. Further, an earpiece (detachable part) having a shape matched with the ear canal when the listener wears the earphone is attached to the other end of the housing (an insertion portion of the ear canal). For example, a canal-type earphone device in which a sound tube is obliquely arranged from a position off the center of a housing, thereby to be arranged up to an ear canal entrance, in addition to the housing being put in a cavum conchae, has been proposed (for example, see Patent Document 1).
Even while the listener wears the earphone and is listening to presented audio, the listener needs to listen to an ambient sound at the same time when people around talks to the listener, for example. However, most of the conventional earphones including the canal-type earphone, it is extremely difficult for the listener to listen to the ambient sound in the wearing state. This is because the conventional earphones have a structure to almost completely block the ear cavity, from the perspective of improvement of reproduced sound quality and prevention of leakage of the reproduced sound to an outside. For example, in doing sports outside and inside, including walking, jogging, cycling, mount climbing, and snowboarding, in driving, or in navigation, being not able to listen to the ambient sound is a dangerous situation. Further, if the ambient sound cannot be heard in communication or presentation, the situation is led to a decrease in service.
Further, the conventional earphone appears to block the ear cavity of the listener in the wearing state, to the people around. Therefore, the wearer of the earphone gives the people an impression of feeling awkward to talk to, and may impede interpersonal communication.